While there are many existing designs for sheet feed mechanisms, one of the more popular designs employed in copiers, facsimiles, etc. is shown in FIG. 1. Sheets 10 to be individually fed, are positioned in a tray 12 and are held in position by separators 14. A D-shaped roller 16 is mounted for rotation on a shaft 18. A single clockwise rotation of D-shaped roller 16 will cause a single sheet 10 to be fed in the direction indicated by arrow 20. D-shaped roller is also called a paper-pick roller.
Shaft 18 is connected to a D-roller gear 22 that has a section 24 wherein the gear teeth have been removed (gear teeth are shown schematically). A mating drive gear 26 is mounted on a drive shaft 28 that is in turn connected to a bi-directional drive motor (not shown).
The portion of shaft 18 to the right of D-roller gear 22 has a radially extending shaft extension 30 which, in cooperation with leaf spring 32 and solenoid 34, enables shaft 18 to make a single revolution and accomplish the feeding of a single sheet. Leaf spring 32 bears against shaft extension 30 and biases it in a clockwise direction. An armature 36 is spring biased to engage control arm 30 and in that position, prevents clockwise rotation of shaft 18.
To enable the feeding of a sheet, solenoid 34 is actuated and withdraws armature 36 from engagement with shaft extension 30. This action frees shaft extension 30 to be acted upon by spring 32. Once shaft extension 30 has just passed armature 36, solenoid 34 is disengaged to enable armature 36 to re-engage shaft extension 30 at the end of a single rotation of D-roller shaft 18. A subsequent energization of the drive motor causes shaft 28 to rotate in a counterclockwise direction, thus enabling drive gear 26 to rotate D-roller gear 22 (and shaft 18) in a clockwise direction. The resulting rotation of D-roller 16 engages a sheet 10 and moves it in the direction shown by arrow 20. When recessed portion 24 of D-roller gear 22 reaches drive gear 26, drive gear 26 and D-roller gear 22 disengage. Armature 36 again engages shaft extension 30 at the end of a single rotation.
Others have attempted to reduce the cost of the sheet feed mechanism shown in FIG. 1 by eliminating solenoid 34 and mounting a slip clutch on shaft 18. The slip clutch is dependent upon controlled friction between the clutch mechanism and drive shaft 18, which friction, if too great, causes drive shaft 18 to bind and if too little, enables the clutch mechanism to slip on the shaft uncontrollably. The slip clutch design also employs fixed stops which tend to generate stick-slip noise and be subject to wear.
Accordingly, it is an object of this invention, to provide an improved sheet feed mechanism that avoids the need for solenoid-operated engagement of a control arm.
It is another object of this invention to provide an improved sheet feeder that avoids the use of a slip clutch to control the feeder's operation.
It is yet another object of this invention to provide an improved sheet feeder that is low in cost and reliable in operation.